Here's something interesting. In 1913 the Queen of Rumania declined an association between her son Frederick and the Grand Duchess Olga, because of hemophilia in Olga's family. She was apparently the first royal to do this.
Below is the a quote from the British Journal of Haematology:
"In the same way that Victoria, with her personal aspirations of a marriage between Alix and the Duke of Clarence, had not considered the possibility of haemophilia, neither did the St Petersburg hierarchy consider a marriage to Nicholas undesirable. Haemophilia was already well recognized in Victoria’s descendants. Her youngest son, Leopold, had already died, as had Frittie her grandson. The inheritance of haemophilia had been known for some time since its description by John Conrad Otto (Otto, 1803).
"However, it was as late as 1913 before the first royal marriage was declined because of the risk of haemophilia, when the Queen of Rumania decided against an association between her son, Crown Prince Ferdinand, and Olga, the eldest daughter of Nicholas and Alexandra. The Queen of Rumania was herself a granddaughter of Queen Victoria and therefore a potential haemophilia carrier!"
British Journal of Haematology 1999, 105, 25–32
Historical Review
THE HISTORY OF HAEMOPHILIA IN THE ROYAL FAMILIES OF EUROPE